Acute Kidney Injury Predisposes to Chronic Dialysis

Action Points

Explain to interested patients that acute kidney injury occurring during hospitalization is a serious complication that can lead to dialysis or death.

Also explain that, even if kidney function normalizes by the time of hospital discharge, the risk for later dialysis remains high.

Hospitalized patients who developed acute kidney injury requiring short-term dialysis were three times more likely than controls to require subsequent chronic dialysis, a Canadian study found.

Among patients with acute kidney injury, the incidence rate of chronic dialysis was 2.63 per 100 person-years, compared with 0.91 among controls, for an adjusted hazard ratio of 3.23 (95% CI 2.70 to 3.86), according to Ron Wald, MD, of the University of Toronto, and colleagues.

However, mortality risk was not significantly different between patients and controls, with an adjusted hazard ratio of 0.95 (95% CI 0.89 to 1.02), the researchers reported in the Sept. 16 Journal of the American Medical Association.

In-hospital mortality rates for patients who develop acute kidney injury requiring dialysis range from 45% to 70%, and 15% of those who survive remain on dialysis when they are discharged, the researchers noted.

However, the long-term outcomes of patients who recover sufficient renal function to be discharged free of dialysis had not been well studied, despite the prognostic and resource allocation implications for these patients -- such as the need for specialist care and planning for dialysis.

So the investigators undertook a retrospective study of all adults admitted to an acute care hospital during a ten-year period who had acute kidney injury and dialysis, matching them with as many as four hospitalized controls.

A total of 3,769 cases and 13,598 controls whose mean age was 62 years were included in the study and followed for a median of three years, beginning 30 days after discharge.

More than half of all study subjects were men, and slightly more than one-quarter of both cases and controls had chronic kidney disease within the previous five years.

The increased risk of chronic dialysis occurred across all patient subgroups, including those with diabetes, heart failure, and cancer. But it was particularly prominent among patients without pre-existing chronic kidney disease (adjusted HR 15.54, 95% CI 9.65 to 25.03).

The incidence rate for all-cause mortality was 10.10 per 100 person-years among patients with kidney injury, compared with a slightly higher 10.83 per 100 person-years for controls. But after adjusting for age and propensity score, the risk of death did not differ between the groups.

The "surprising trend" of a slightly lower associated risk of death among patients with kidney injury may be explained by the observation that lifesaving therapies are more likely to be given to patients who have favorable prognoses.

In addition, for some 7% of cases, no matched controls could be found, and these cases were excluded from the data analysis.

Those patients had a higher mortality rate over time (14.18 per 100 person-years), and if they had been included in the analyses the trend toward lower mortality among cases would have been further attenuated.

"Injury to the kidney, especially that necessitating acute dialysis, seems to independently predispose a patient to long-term dialysis, even among those who are free of dialysis at hospital discharge," the investigators wrote.

This may result from loss of renal vasculature and the development of fibrosis following ischemia-reperfusion injury.

The finding that patients with acute kidney injury remain at high risk for dialysis over the next three to five years suggests that these patients may benefit from specialized care and concerted efforts to prevent progression, according to the investigators.

Limitations of the study included reliance on administrative data, which may have permitted misclassification of patients, and the unavailability of measures of kidney function.

An editorial accompanying the study echoed concern about use of administrative data.

"Chronic kidney disease is poorly identified by administrative data, with reported sensitivities of less than 25%," wrote Sushrut S. Waikar, MD, of Harvard Medical School, and Wolfgang C. Winkelmayer, MD, of Stanford University School of Medicine.

And, even though comparable proportions of cases and controls had pre-existing chronic kidney disease, it was not possible to determine if their actual renal function was comparable, the editorialists noted.

Reliance on administrative data also may help explain the contradictory findings of higher risk for chronic dialysis but slightly risk or mortality, they wrote, noting the possibility of greater comorbidities or severity of illness among controls.

Still, Waikar and Winkelmayer concluded, "Given the extraordinarily high rates of morbidity and mortality observed in chronic kidney disease patients and acute kidney injury patients, the complex interconnection between them, and increasing incidence of both, kidney disease prevention and treatment should be a major public health priority."

The study was supported by the Institute for Clinical Evaluative Sciences and the University of Toronto Faculty of Medicine.

Wald reported receipt of an award from the Canadian Institutes of Health Research and an unrestricted grant from Amgen.

Co-authors Damon Scales, MD, Robert Quinn, MD, and Joel Ray, MD, reported support from the Canadian Institutes of Health.

Winkelmayer reported support from the National Institutes of Health, the American Heart Association, Satellite Healthcare, and Amgen and sits on the advisory boards of several pharmaceutical companies.